Environmental abiotic stresses, including drought stress, cold stress, freezing stress, heat stress and salinity stress are major factors limiting plant growth and productivity. Crop losses and reduction in yield of major crops including maize, wheat and rice caused by such stresses represent significant economic issues and also lead to food shortages in several underdeveloped countries.
The development of stress tolerant plants has the potential to reduce or solve at least some of these problems. The use of traditional plant breeding strategies to produce new lines of plants that exhibit tolerance to these types of stresses has been slow. Lack of sufficient germplasm resources, and incompatibility between distantly related plant species, present significant problems in conventional breeding. Further, the cellular processes leading to tolerance to such stresses are complex and involve multiple mechanisms of cellular adaptation and numerous metabolic pathways. This limits the success of both traditional breeding and that of genetic engineering approaches to development of stress tolerant plants. It would be beneficial to identify genes and proteins involved in controlling the complex processes leading to stress tolerance.
Regulators of gene expression, such as transcription factors, involved in controlling stress tolerance may be particularly useful in genetic engineering of plants, as a single gene may control a whole cascade of genes leading to the tolerance phenotype. Furthermore, there is sometimes commonality in many aspects of the different types of stress tolerant responses referred above. For example, genes that increase tolerance to cold or salt may also improve drought stress tolerance. This has been demonstrated in the case of the transcription factor At CBF/DREB 1 (Kasuga et al., 1999 Nature Biotech 17: 287-91) and the vacuolar pyrophosphatase AVP1 (Gaxiola et al., 2001 PNAS 98:11444-19).
Whilst some potentially useful genes have been identified, the identification and cloning of plant genes that confer tolerance to stress remains fragmented and incomplete. Although it is assumed that stress induced proteins may have a role in stress tolerance, evidence is still lacking and the function of many such stress responsive genes is unknown.
The hot and dry weather conditions in New Zealand and other countries in the summer period can have significant effect upon the yield of ryegrass. This is invariably during the dairy milking season and therefore has real effects on cost of dairy production through either reduced milk yield or the use of supplementary feeds and/or irrigation systems.
It would be beneficial to identify genes which have the capacity to confer stress tolerance in stress susceptible plant species. The development of stress tolerant crops will provide many advantages such as increasing yield and producing plants that may be cultivated in previously unsuitable environmental conditions. Thus, there exists a need for compositions and methods for producing plants with improved stress tolerance relative to cultivated counterparts.
It is an object of the invention to provide improved compositions and methods for developing plant varieties with improved tolerance to at least one of the following stresses; drought, cold, freezing, heat and salinity, or at least to provide the public with a useful choice.